What Is a Blackhead?
A Blackhead Is a Small, Dark-colored Clogged Pore
Blackheads, also called open comedones, are small, non-inflammatory, black- or brown-colored clogged pores that most often develop on the face. They develop when a pore becomes partially clogged by skin cells and begins to fill up with skin oil. Because the pore is only partially blocked, oxygen from the air seeps in and reacts with melanin in the clogged pore. It is not dirt, but rather this chemical reaction, that causes the black or brown color we see with blackheads.
Open comedones (blackheads) are brown- or black-colored comedones (clogged pores) that mainly form on the face, but can also be found on the neck, back, chest, shoulders, and upper arms. Dermatologists classify blackheads as "non-inflammatory" acne lesions because they are not red, swollen, or painful.
Blackheads form when microscopic hair follicles, often called pores, become partially clogged by skin cells and skin oil (sebum). Once a blackhead develops, it can remain on the skin for several weeks or even months, after which it either resolves on its own or develops into a red, swollen, sore "inflammatory" acne lesion.
Most people develop blackheads during their teenage or young adult years, but developing them at an older or younger age is also common.1
How Blackheads Develop
Blackheads develop in two steps.
1. Blockage of a hair follicle and formation of a microcomedone
All acne lesions begin with microscopic hair follicles in the skin, called pores. Attached to these pores are glands, called sebaceous glands, which produce skin oil, called sebum. Normally, sebum is expelled onto the surface of the skin. However, in acne, the opening to the hair follicle becomes clogged with skin cells, and this results in a clogged pore, called a comedone. Scientists believe that a combination of inflammation, hormone levels, and excessive sebum production contributes to clogging the hair follicle. When the hair follicle first becomes clogged, the lesion is called a microcomedone, and it cannot be seen with the naked eye.
2. Formation of a comedone
After a microcomedone forms, the sebum, which is unable to escape the hair follicle, begins to accumulate inside the pore. As more sebum builds up inside the pore, the microcomedone grows larger and becomes a visible comedone. There are two types of comedones: blackheads and whiteheads.
- Blackheads are called open comedones, because the opening of the pore is only partially blocked. This means that sebum can still escape the pore to some degree, and that oxygen, from the air, can enter into the pore. The air that enters the pore interacts with the sebum inside the pore, causing a chemical reaction called oxidation, which is responsible for the characteristic black or brown hue of a blackhead. Once developed, a blackhead can remain on the skin for several weeks or longer.2
- Whiteheads are called closed comedones, because the opening of the pore is completely blocked, and nothing can enter or leave the pore. When the sebum cannot escape the pore, it accumulates, and this buildup of sebum gives the whitehead its characteristic white or skin-colored hue. Once developed, a whitehead remains on the skin for several days.2
How Long Do Blackheads Remain on the Skin?
A 1974 study published in the Journal of Investigative Dermatology found that blackheads, on average, remain on the skin between 45 and 60 days, but can last up to at least 98 days. After this time, a blackhead will either resolve on its own or develop into an inflammatory acne lesion.3
What Causes Blackheads?
Scientists believe that several factors contribute to the development of a blackhead.4-9
- Inflammation: Inflammatory molecules have been found in blackheads, although they are classified as "non-inflammatory" acne lesions. One study found that the inflammatory molecule interleukin 1 (IL-1) is found in up to 76% of comedones, including both blackheads and whiteheads. This suggests that although blackheads are not red, sore, or swollen, there is almost always inflammation present in them and that it likely plays a role in their development.
- Hormones: Increased hormones, especially androgens, play a major role in the development of acne. In fact, without hormones, acne will not develop. So increased levels of androgens, which can be found in both males and females, can result in more blackheads.
- Accumulation of skin cells: Skin cells known as keratinocytes are constantly produced and shed from the skin. In acne, an accumulation of both new skin cells and dead skin cells occurs along the wall of the hair follicle, leading to the development of blackheads and whiteheads.
- Keratin: Keratin is an especially sticky protein normally produced by keratinocytes. As there is an accumulation of these cells in the hair follicle, there is also an accumulation of keratin. The keratin causes the skin cells to stick together, facilitating the development of a comedone.10,11
Blackheads, also known as open comedones, are small, non-inflammatory, black- or brown-colored comedones that most often develop on the face. They develop when a pore becomes clogged by skin cells and begins to fill up with sebum. Blackheads remain on the skin for several weeks or months before either resolving on their own, or developing into an inflammatory lesion, such as a papule, pustule, nodule, or cyst.
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- Orentreich, N. & Durr, N. The natural evolution of comedones into inflammatory papules and pustules. J Investig Dermatol 62, 316 - 320 (1974).
- Do, T. et al.Computer-assisted alignment and tracking of acne lesions indicate that most inflammatory lesions arise from comedones and de novo. J Am Acad Dermatol 58, 603 - 608 (2008).
- Danby, F. Ductal hypoxia in acne: Is it the missing link between comedogenesisand inflammation? J Am Acad Dermatol 70, 948 - 949 (2014).
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